Some aspects of EMS-induced mutagenesis in Escherichia coli

AB2497 and its mutS and umuDC derivatives were EMS-treated at the stationary phase and specificity of mutation measured. It was found that: (i) in mutS⁺ cells EMS induces predominantly GC → AT transitions (by supB or supE(oc) formation) and in mutS⁻ cells mainly AT → TA transversions (by supL(NG) formation); (ii) transversions of AT → TA are umuDC-dependent and mutational specificity is biased towards AT → GC transitions in mutS⁻umuDC⁻ strains. When mutS⁻umuDC⁻ cells were transfected with plasmids bearing umuD'C or umuDC genes, mutational specificity was again biased towards AT → TA transversions; (iii) experiments with bacteria bearing umuC::lacZ or recA::lacZ fusions suggest that processing of UmuD → UmuD' might be poorer in EMS-treated mutS⁻ than in mutS⁺ cells.